Seed Formation Samuel Contreras Departamento de Ciencias Vegetales Pontificia Universidad Catolica de Chile scontree@uc.cl
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1. Floral Induction
1. Floral induction
INTRODUCTION Plant Life Cycle
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1. Floral induction Seed Juvenile Plant Zygote
Life cycle of a seed propagated plant
Flower
Transition
Adult Plant
1. Floral induction Embryonic phase
Seed Juvenile Plant
Zygote
Life cycle of a seed propagated plant
Flower
Transition
Adult Plant
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1. Floral induction Embryonic phase
Juvenile vegetative phase
Seed
Juvenile Plant Zygote
Life cycle of a seed propagated plant
Flower
Transition
Adult Plant
1. Floral induction Embryonic phase
Juvenile vegetative phase
Seed
Juvenile Plant Zygote
Life cycle of a seed propagated plant
Flower
Transition
Adult Plant
Adult vegetative phase
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1. Floral induction Embryonic phase
Juvenile vegetative phase
Seed
Juvenile Plant Zygote
Life cycle of a seed propagated plant
Flower
Adult reproductive phase
Transition
Adult Plant
Adult vegetative phase
1. Floral induction Phase changes in Ivy (Hedera helix):
from Hartmann and Kester’s Plant Propagation: Principles and Practices, 7th edition (2002).
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1. Floral induction - Juvenile vegetative phase • Plants are insensitive to stimuli that promote flowering and they cannot flower
Carrot example
Juvenile vegetative phase
Adult vegetative phase
First growing season
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Carrot example
Juvenile vegetative phase
Adult vegetative phase
First growing season
winter
Adult reproductive phase Second growing season
1. Floral induction - Juvenile vegetative phase • Plants are insensible to stimuli that promote flowering and they cannot flower • Duration variable among and within species
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Age of flower development in some woody plants in the seedling phase. Species
Length of juvenile period
Rose (Rosa spp.)
20-30 years
Grape (Vitis)
year
Apple (Malus spp.)
3-8 years
Citrus (Citrus spp.)
5-8 years
Scotch pine (Pinus sylvestris)
5-10 years
Ivy (Hedera helix)
5-10 years
Redwood (Sequoiadendron giganteum)
20 yeasr
Oak (Quercus robur)
25-30 years
Beech (Fagus sylvatica)
30-40 years
from Hartmann and Kester’s Plant Propagation: Principles and Practices, 7th edition (2002).
Carrot example Transition
Competent plant
Juvenile vegetative phase
Adult vegetative phase
First growing season
winter
Adult reproductive phase Second growing season
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Carrot example
Low Temperatures VERNALIZATION
Transition
Competent plant
Juvenile vegetative phase
Adult vegetative phase
First growing season
winter
Adult reproductive phase Second growing season
Determined meristem in carrot:
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1. Floral induction External factors affecting flowering • Photoperiod (day length) • Temperature (vernalization)
1. Floral induction
Photoperiod (day length)
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Effect of latitude on day length at different times of the year. Day length was measured on the 20th of each month (from Taiz & Zeiger, 2002)
1. Floral induction - Photoperiod Three main categories:
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1. Floral induction - Photoperiod Three main categories: •Short day (SD) plants: flowering promoted by days that are shorter than a critical day length.
1. Floral induction - Photoperiod Three main categories: •Short day (SD) plants: flowering promoted by days that are shorter than a critical day length. •Long day (LD) plants: flowering promoted by days that are longer than a critical day length.
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1. Floral induction - Photoperiod Three main categories: •Short day (SD) plants: flowering promoted by days that are shorter than a critical day length. •Long day (LD) plants: flowering promoted by days that are longer than a critical day length. •Day neutral plants: flowering under any photoperiodic condition.
1. Floral induction - Photoperiod Three main categories: •Short day (SD) plants •Long day (LD) plants •Day neutral plants - Qualitative (yes or no) - Quantitative (sooner or later; more or less)
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1. Floral induction - Photoperiod Three main categories: •Short day (SD) plants •Long day (LD) plants •Day neutral plants •Long-short day plants •Short-long day plants
(from Taiz & Zeiger, 2002)
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(from Taiz & Zeiger, 2002)
1. Floral induction
Vernalization (temperature)
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(from Taiz & Zeiger, 2002)
Carrot example
Low Temperatures VERNALIZATION
Transition
Competent plant
Juvenile vegetative phase
Adult vegetative phase
First growing season
winter
Adult reproductive phase Second growing season
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(from Copeland and McDonald, 2001)
Devernalization: loss of vernalization response, usually by exposure to high temperatures
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(from Taiz & Zeiger, 2002)
1. Floral induction - vernalization
Æ Photoperiod x vernalization interaction
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1. Floral induction Chemical stimuli • Natural and synthetic
1. Floral induction Chemical stimuli • Natural and synthetic • Gibberellins (GA)
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1. Floral induction Chemical stimuli • Natural and synthetic • Gibberellins (GA) • Others: indoleacetic acid, cytokinins, ethylene, naphtaleneacetic acid, 2,4- dichlorophenoxyacetic acid, ethylene chlorohydrin, acetylene, and 2,3,5triidobenzoic acid.
2. Floral morphology
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RECEPTACLE
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PETAL
SEPAL
RECEPTACLE
PETAL (COROLLA)
SEPAL (CALYX)
RECEPTACLE
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PETAL (COROLLA) PERIANTH TEPALS
SEPAL (CALYX)
RECEPTACLE
STAMENS (ANDROECIUM) ANTHER
FILAMENT
PETAL (COROLLA) PERIANTH TEPALS
SEPAL (CALYX)
RECEPTACLE
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STAMENS (ANDROECIUM) ANTHER
FILAMENT
STIGMA
STYLE
PETAL (COROLLA)
PISTIL SINGLE CARPEL (GYNOECIUM)
PERIANTH TEPALS
SEPAL (CALYX)
OVARY
RECEPTACLE
Figure 2.1 from Bradford
Floral Meristems develop inward from the outer whorl.
(from: Bradford, K. 2004. Seed Production and Quality. Course syllabus, spring 2004).
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STAMENS (ANDROECIUM) ANTHER
FILAMENT
Stamen:
Anther
Pollen sac
Filament
More than one carpel: One carpel:
Ranunculus
Rosa
Solanum
Cornus
From Esau, 1977.
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More than one carpel: One carpel: Apocarpus gynoecium (separated carpels)
Solanum
Ranunculus
Rosa
Cornus
From Esau, 1977.
More than one carpel: One carpel: Apocarpus gynoecium (separated carpels)
Ranunculus
Rosa
Syncarpus gynoecium (fused carpels)
Solanum
Cornus
From Esau, 1977.
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More than one carpel: One carpel: Apocarpus gynoecium (separated carpels)
Syncarpus gynoecium (fused carpels) Pistil
Pistil
Ranunculus
Pistil
Rosa
Solanum
Cornus
From Esau, 1977.
One carpel: STIGMA
STYLE
Pistil
OVARY
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The Ovary: Seed
Ovary wall
One carpel
Placenta Locular cavity
parietal
axile
free central
(from Raven et al. 1999)
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Flower classification:
- Complete flowers have sepals, petals, stamens, and carpels.
- Incomplete flowers, at least one of those structures is not present.
Flower classification:
Imperfect flower
Perfect flower
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Examples of hermaphrodite plants:
Tomato
Pepper
Example of a monoecious plant (maize):
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Example of a dioecious plant:
Asparagus, male plant
Asparagus, female plant
Andromonoecious plant:
Gynomonoecious plant:
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(from Raven et al., 1999)
3. Pollen and ovule formation
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3. Pollen and ovule formation
Pollen formation Microsporogenesis: formation of microspores (single celled pollen grains)
Microgametogenesis: formation of the microgametophyte within the pollen grain
Microsporogenesis: Anther: epidermis vascular bundle
Microspore mother cells or microsporocytes tapetum
(from Raven et al. 1999)
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Microsporogenesis:
Microspore mother cell (2n)
each one becomes a uninucleate microspore with haploid nucleus
Four haploid (1n) cells
Microgametogenesis: Two haploid nuclei: Vegetative nucleus Generative nucleus
(from Raven et al. 1999)
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Microgametogenesis: V
Mitosis generative cell Binucleate pollen grain after microspore mitosis v: nucleus
of the vegetative cell g: nucleus of the generative cell s: nucleus of the sperm cell
Trinucleate pollen cell, with two sperm cells (s) from the mitosis of the generative cell (g)
from Mascarenhas, 1989. The Plant Cell (1): 657- 664
Mature pollen grain: intine vegetative nucleus
exine
generative nucleus Two-celled pollen grain of Montropa uniflora (Esau, 1977)
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3. Pollen and ovule formation
Ovule formation Megasporogenesis: formation of a megaspore Microgametogenesis: formation of the megagametophyte (embryo sac)
Megasporogenesis: nucellus
megasporocyte (2n)
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Megasporogenesis: nucellus
megasporocyte (2n)
Meiosis I
Meiosis II
four haploid megaspores
Megasporogenesis: nucellus
megasporocyte (2n)
Meiosis I
three megaspores degenerate
Meiosis II
four haploid megaspores
functional megaspore
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Megagametogenesis:
functional megaspore
Mitosis I
Mitosis II
Mitosis III
Megagametogenesis: Embryo sac, megagametophyte or female gametophyte
functional megaspore
Mitosis I
Mitosis II
Mitosis III
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Megagametogenesis: Embryo sac:
antipodal cells
central cell
two pollar nuclei egg cell egg cell vacuole
egg apparatus
synergid cells
Ovule formation: Example of the development of an anatropous ovule:
nu: nucellus ms: megasporocyte ii: inner integument oi: outer integument
fu: funiculus fm: functional megaspore dm: degenerative megaspore
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Ovule formation:
chalaza
Example of an anatropous ovule
nucellus embryo sac
outer integument inner integument micropyle
funiculus
4. Pollination and fertilization
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4. Pollination and fertilization Pollination: transfer of pollen from the anther to stigma
stigma
pollen grain
anther style filament pollen grains
sperm cells
ovary
pollen tube
4. Pollination and fertilization Pollination: transfer of pollen from the anther to stigma
Self-pollination
Cross-pollination
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4. Pollination and fertilization Types of plant species according to the frequency of self- or cross-pollination: • Self-pollinated or autogamous
• Cross-pollinated or allogamous
4. Pollination and fertilization Pollination may be assisted by physical (water, wind) or biological (insects, birds, mammals) vectors.
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4. Pollination and fertilization
pollen grain
sperm cells pollen tube
4. Pollination and fertilization
(from Raven et al. 1999)
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Double fertilization:
from Copeland and McDonald, 2001
5. Embryogenesis
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Embryogenesis in dicotyledonous species (example Capsella bursa-pastoris) distal end (axial or apical; closer to chalazal end)
suspensor
basal end (closer to micropyle end)
Embryogenesis in dicotyledonous species (example Capsella bursa-pastoris)
embryo, globular stage
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Embryogenesis in dicotyledonous species (example Capsella bursa-pastoris)
embryo, heart stage
Embryogenesis in dicotyledonous species (example Capsella bursa-pastoris)
embryo, torpedo stage
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Embryogenesis in dicotyledonous species (example Capsella bursa-pastoris)
Embryogenesis in monocotyledonous
two cell stage
proembryo
from Copeland and McDonald, 2001
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Embryogenesis in monocotyledonous
two cell stage
proembryo
from Copeland and McDonald, 2001 (from Raven et al. 1999)
Embryogenesis in monocotyledonous
two cell stage
proembryo
from Copeland and McDonald, 2001 (from Raven et al. 1999)
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plumule epicotyl hypocotyl
testa
radicle
pericarp testa aleurona layer endosperm scutellum (cotyledon) coleoptile plumule apical meristem
embryo
first leaves
scutellar node radicle coleorhiza
cotyledon
APICAL MERISTEMS plumule epicotyl hypocotyl testa
radicle
pericarp testa aleurona layer endosperm scutellum (cotyledon) coleoptile plumule apical meristem
embryo
first leaves
scutellar node radicle coleorhiza
cotyledon
APICAL MERISTEMS
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(from Raven et al. 1999)
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6. Endosperm and perisperm development
Endosperm development: A. Ovule after fertilization:
B. Cellular endosperm
C. Nuclear endosperm
D. Helobial endosperm
from Copeland and McDonald, 2001
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Æ Bean seed. No endosperm present in mature seed.
first leaves
plumule epicotyl hypocotyl
testa
radicle
cotyledon
Lettuce seed (achene) (from Esau, 1977)
Pepper seed
Drawing showing a mature seed of Capsicum annum (Color image by Katrin Hermann based on an EM image by Watkins and Cantliffe, Plant Physiol 72: 146-150, 1983). Color drawing published in Finch-Savage and Leubner-Metzger (2006).
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Ricinus communis seed: endosperm testa cotyledons plumule
Wheat seed (caryopsis)
embryo
hypocotyl radicle
(from Esau, 1977)
Perisperm: diploid tissue that originates from the nucellus
Sugar beet (Beta vulgaris L.) seed
endosperm
testa
perisperm
Hypocotyl cotyledons radicle
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- Albuminous seed
- Exalbuminous seed
7. Seed coat
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7. Seed coat Mature seed:
Embryo sac:
outer integument inner integument
testa
seed coat
7. Seed coat Mature seed:
Embryo sac:
outer integument iner integument
Ovary wall
testa
seed coat
+ perisperm
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Integuments functions during seed development: • Pathway for transport and conversion • Temporary storage • Involvement in gas exchange • Supply of growth compounds • Protection
Seed coat functions in mature seed: • Protection • Assistance in dispersion • Water uptake regulation • Seed dormancy regulation
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7. Seed coat Æ Seed coat structure
7. Seed coat Æ structure
Drupe:
Nut:
endocarp
Shagbark Hickory (Carya ovata)
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Caryopsis:
Achene:
7. Seed coat Æ structure
first leaves
plumule epicotyl hypocotyl
testa
radicle
Bean seed:
micropyle hilum
cotyledon
raphe
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Pumpkin seed cross section
Soybean seed cross section
(from Esau, 1977)
8. Fruit development
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7. Fruit development Example tomato: Fruit (mature ovary): Flower:
ovary
ovary wall Æ pericarp
7. Fruit development
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7. Fruit development Peach:
7. Fruit development Peach:
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Fruit classification: • Simple fruits
• Aggregate fruits
• Multiple fruits
Fruit classification: • Simple fruits
Fleshy Dry
• Aggregate fruits
• Multiple fruits
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Fruit classification: • Simple fruits
Fleshy Dry
Dehiscent Indehiscent
• Aggregate fruits
• Multiple fruits
Simple dry indehiscent fruits, examples: Achene
Nut
Caryopsis
Samara
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Simple dry dehiscent fruits, examples: Capsule
Pod
Silique
Samara
Simple fleshy fruits, examples: Drupe
Berry
Pepo
Samara
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Fruit classification:
Strawberry:
• Simple fruits
• Aggregate fruits individual seed (achene) raspberry
• Multiple fruits
Fruit classification: • Simple fruits
• Aggregate fruits
• Multiple fruits Pineapple
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9. Seed structure (summary)
FRUIT
OVARY OVULE INTEGUMENTS NUCELLUS EGG NUCLEUS + SPERM NUCLEUS
SEED TESTA PERISPERM
ZYGOTE (2n) EMBRYO
2 POLAR NUCLEI + SPERM NUCLEUS
ENDOSPERM (3n)
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first leaves
plumule epicotyl hypocotyl
testa
radicle
cotyledon
pericarp testa aleurone layer endosperm scutellum (cotyledon)
apical meristem
embryo
coleoptile plumule
scutellar node radicle coleorhiza
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endosperm
testa
perisperm
Hypocotyl cotyledons
radicle
endosperm testa
cotyledons plumule
embryo
hypocotyl radicle
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10. Apomixis and polyembryony
i: integuments f: funiculus m: micropyle es: embryo sac F: double fertilization from: Kultunov and Grossniklaus, 2003. Annu. Rev. Plant Biol. 54: 547-574
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i: integuments f: funiculuc m: micropyle es: embryo sac F: double fertilization from: Kultunov and Grossniklaus, 2003. Annu. Rev. Plant Biol. 54: 547-574
Polyembryony: simultaneous formation of more than one embryo within a seed.
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